CHAIN_BLK_FLAG
WARN_ON_ONCE(!(next & CHAIN_BLK_FLAG));
next &= ~CHAIN_BLK_FLAG;
chain_hlocks[offset] = (next >> 16) | CHAIN_BLK_FLAG;
BUILD_BUG_ON((MAX_LOCKDEP_KEYS-1) & CHAIN_BLK_FLAG);